How do you use an AIO as an external monitor? Well, I must say it is not easy since manufacturers have quite a few model lines and configured them a bit differently so owners and users who knew one way are stumped when it fails to work on another system. Second, the source (or video connections) can be from a computer, laptop, game console, or another AIO that is daisy-chained and the proper casting must be used to prevent a no signal which is basically a black screen.
★ HDMI IN on the target AIO (for accepting the A/V signal)
★ HDMI Cable (for Audio and Video transfer) or
★ DP to HDMI Cable (for Audio and Video transfer)
★ Video Source (another AIO, desktop/mobile computer, game console).